CAD computer aided design meaning

 

 

 

CAD computer aided design meaning

 

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CAD computer aided design meaning

Computer‑aided design, or CAD as it is more commonly known, has grown from a narrow activity and concept to a methodology of design activities that include a computer or group of computers used to assist in the analysis, development, and drawing of product components. The original CAD systems developed and used in industry could more realistically be classified as computer‑aided drafting systems. However, the benefits of using basic geometric information for structural analysis and planning for manufacturing were quickly recognized and included in many CAD systems. Today, as in the past, the basis for CAD is still the drafting features or interactive computer graphics (ICG) that these systems were originally designed to perform. However, the scope of these systems has taken on a new meaning. A typical CAD system is illustrated in Figure 17.1. As can be seen, the graphics display portion of the system is the most noticeable feature. Computational processes have, however, been added to the system for increased capabilities.

In general, there are four basic reasons for implementing CAD system!

1.  A reduction in design time. The total time required from inception of an idea to its complete specification can be reduced by an order of magnitude by using easily alterable geometric models. Design perturbations/changes can be completed in minimal time. Whole scenarios of design possibilities can be constructed quickly.

2.  Improved product design. Because CAD systems allow the designer to alter the product without major redrawing with considerable time commitment , many final designs can be constructed in a reasonable period of time. Similarly, these designs can be automatically analyzed for structural characteristics by using computer‑aided engineering (CAE) software such as finite‑element modeling (FEM).

3.  Improved information access. Because CAD drawings are stored in a large computer database, they can be accessed quickly and easily. Parts can be coded on the basis of geometric shape, and similar parts can be called up to assist in the design and specification of new parts. "Standard parts" can be employed whenever possible, rather than having to re‑invent the wheel over and over again.

4.  Manufacturing data creation. With the advent of numerical control (NC) came the need to automatically generate the tool path required for machining. Since the part geometry dictates the machining required, knowing the part shape can allow for (semi‑)automatic part‑program preparation. CAD data can also be used for automated process planning.

              It is interesting to note that twenty years ago if a part of reasonable geometric and manufacturing sophistication was created, hundreds of design and drafting hours would be required. After the part was specified, manufacture would begin. This planning would normally require some minor design changes (back to the designer and draftsman), and might take as long as the original design process. Special tooling, fixturing, etc., might also be specified during the planning for manufacture. In all, the entire process of product and process design could take several weeks or months. With today's CAD systems, designing (again a reasonably sophisticated component) and generating manufacturing plans, preparing part programs and producing the part is possible in days rather than weeks. In general, the total engineering and manufacturing time has been cut markedly using integrated CAD/CAM methodologies.

 

USING CAD FOR MANUFACTURED COMPONENT DESIGN

Although CAD represents the integrated use of a computer in the design process, the use of CAD does not change the design process requirements. As in the past, the designer is still responsible for

1.  Developing the geometric detail required for the product (shape, dimen­sion, tolerance, etc.)
2.  Performing the necessary analysis on the design
3.  Reviewing and altering the design on the basis of functional and economic characteristics
4.  Communicating the design via an understandable drafting system

Independent of whether a CAD system was employed in the design or whether the designer used a standard drafting table, each of these design steps must be addressed either formally or informally. An example of these activities would be an engineer who needs a special wrench to adjust a positioning nut that is located in a place not accessible using a standard straight‑shank tool. Several bends must be manufactured into a standard open‑end wrench.

In order to obtain the wrench in the most expeditious manner, the engineer would most likely walk to the tool fabrication shop and explain his needs to one of the machinists. If the number of bends required in the wrench are few and simple, the engineer may simply explain his needs verbally to the machinist. Using this description, the machinist may be able to understand the geometric requirements and select the material based on the physical require­ments (maximum torque conditions, length of the shaft, etc.). Without a drawing ever being made, the part may be designed and conveyed in the heads of the engineer and machinist and never take form on paper. As the part is being bent, the machinist may alter his initial conception of the part to ease the manufacturing requirements.

As the complexity of the part increases, the likelihood of the process requiring a sketch or drawing also increases. If a very complex tool was necessary, then a detailed engineering drawing with specific tolerances would be required.

 

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CAD computer aided design meaning